1. Field of the Invention
The invention relates generally to the creation of logical volumes, and more specifically, relates to addressing performance variations that may exist across the logical volumes.
2. Discussion of Related Art
Storage systems typically include one or more host systems that are coupled with one or more storage devices. The host systems communicate with the storage devices via storage controller(s) to persistently store data on the storage devices. Storage space on the one or more storage devices may be allocated to provision storage capacity for one or more logical volumes. Logical volumes are a type of virtualized storage that may include a portion of one storage device or span across portions of multiple storage devices.
When a single storage device includes multiple logical volumes, variations may occur in the performance characteristics between the logical volumes based on where on a hard disk of the storage device the logical volumes are stored. The performance across the logical volumes is not normalized, or consistent between the logical volumes. This may primarily be due to variations in the read and write media rates associated with different portions of the rotating magnetic disks used to store the data for the logical volumes. Generally, the read and write media rates in a rotating magnetic disk system vary depending on the position of the read/write heads relative to a spindle at the center of the magnetic disk. For a fixed rotational rate and bit density, tracks along the radial outer edge of the magnetic disk have a higher performance characteristic than tracks along the radial inner edge of the magnetic disk, due to differences in the linear velocity of the disk relative to the read/write heads. Thus, different logical volumes on a storage device may exhibit different performance characteristics. This may also occur in cases where multiple logical volumes are striped across multiple storage devices in that each storage device may exhibit the same performance characteristic variations. Further, some recent developments in disk drives have incorporated flash memory components in addition to the traditional rotating magnetic (or optical) storage medium. In some such devices, the flash memory is merely used as a cache memory. However, in some such devices, the flash memory is a high performance portion of the total capacity of the storage device and represents a portion of the addressable range of logical blocks of the device. Thus, some such newer disk drives incorporating a hybrid of rotating storage media and flash memory storage media may exhibit still further performance characteristic variations.
Variations in the performance characteristics across multiple logical volumes may be problematic regardless of whether the logical volumes passively store data for the host systems or actively participate in booting and running the host systems. For example, a storage device may include a dozen or so bootable logical volumes that are each associated with a different host system. The respective host system boots an operating system from its respective logical volume during operation. However, problems may occur as each host system attempts to access its respective logical volume on the storage device. Problems related to data starvation (where some host systems experience slow read/write times at the storage device), excessive read/write head movement (as the storage device attempts to read data from different radial locations on the disk relative to the spindle), etc., may occur as the host systems attempt to access their respective logical volumes.
Thus it is an ongoing challenge to normalize the read/write storage performance across multiple logical volumes stored on a storage device.